It’s the key to great salad dressings. But despite all the online recipes hailing it as the ultimate homemade weed killer, vinegar is usually better off staying on the kitchen shelf.
Just because there’s a wealth of vinegar herbicide recipes doesn’t mean they all work — or even that the ones that do are worth the effort.
Darren Strenge is Plant Health Manager and Moss Garden Manager at the Bloedel Reserve in Washington State, and also a contributor to West Sound Home & Garden magazine. Asked if using vinegar for weed control seemed worth it in the long run, he replies, “Mostly, I would say, ‘No.’”
“The repeated sprays of salt-containing [vinegar weed killer] recipes can lead to too much soil salt build-up, and recipes that use [kitchen vinegar] but leave out the salt are nowhere near as effective.”
Regardless, seemingly simple, safe, and “natural” vinegar weed killer recipes are popular with organic gardeners and sustainable-lawn lovers, or anyone else thirsty for environmentally friendly ways to save time pulling weeds.
But the science is in and experts have spoken: Using vinegar to kill weeds just isn’t worth it. For one, it may not be the effective weed killer you had hoped for. And some vinegar weed killers could even be dangerous.
Why the Evidence Isn’t There
Despite the abundance of how-to vinegar herbicide recipes online, there are no scientific tests or trials showing the veracity of how well kitchen vinegar works to kill weeds — and that’s only one red flag for would-be vinegar users.
Organic gardening websites and homesteader blogs are prone to powerful personal testimonies of their own success with vinegar. This can add to vinegar’s mystique, but also to its misleading hype.
When you steer away from anecdotal evidence and look at more expert sources, you’ll find that vinegar’s virtues are very much a mixed bag. The University of Maryland Extension, for example, lists that there are far more cons than pros to using it. In summary, these are:
- Kills weeds rapidly, causing death in 24 hours.
- Effective for killing small seedling-stage annual broadleaf weeds.
- Vinegar biodegrades and breaks down quickly (not salts, however).
- Permanently kills only broadleaf weeds; grasses and perennials grow back.
- Only kills above-ground growth, root systems are unaffected.
- Needs multiple applications to be effective.
- Nonselective, will harm or kill your good plants if applied; drift can be harmful to your garden and flower beds.
- The odor may be unpleasant.
- Vinegar may tarnish metal equipment, requires cleaning after application.
- Should not be sprayed on reactive metal (aluminum, tin, iron).
- Though multiple applications needed, should not be applied more frequently than every two weeks.
- Can irritate skin and trigger an allergic reaction; frequent exposure may cause chronic bronchitis, dermatitis and erosion of teeth.
The above list applies only to “horticultural vinegar pesticides” (containing at least 20% acetic acid, the corrosive chemical that kills weeds). These are much stronger than the grocery store-bought white or apple cider vinegars (containing only 5%).
As such, this could indicate that household vinegars are even less reliable at killing weeds than what the above list depicts.
The Home Recipes That Do Work
Experts including Strenge, however, will say kitchen vinegar recipes do work in some capacity, but only in some ways and with limits.
“Vinegar weed killers can work if used properly,” he said, “as long as users understand repeated sprays will be necessary, and that there are potential problems with using vinegar weed killers in their gardens.”
The one homemade recipe Strenge has seen work in action: 1 gallon of vinegar (5% acetic acid) mixed with 1 cup salt and 1 tablespoon dish soap, with an emphasis on the salt making its low concentration effective.
“It will burn weeds on contact under the right conditions: warm, dry, sunny days,” he said. Put it in a spray bottle and aim carefully.
But again, this comes with a caveat. “Users should be aware, however, that just because the ingredients are mostly harmless to humans and larger animals, it doesn’t mean those ingredients can’t be detrimental to the environment and other forms of life,” he said.
At another point, Strenge added, “I don’t really recommend using vinegar and salt weed killers [often] because of potential problems from repeated use.”
Why Vinegar Weed Killers Can Be Dangerous
When you hear “organic” or “natural weed killer,” it’s an easy trap to believe vinegar is entirely safe. Right? Wrong. Vinegar’s corrosive substance, acetic acid (the chemical that does your weed killing for you), apparently comes with some risks.
If not careful, acetic acid can cause burns, permanent damage to skin and tissues, and even blindness if accidental contact is made with the eyes.
Here’s the risk some users take: upon finding their 5% homemade vinegar recipes don’t work as well, they might be tempted to jump up to the 20% concentration, not realizing they’re dealing with real-deal chemicals.
Strenge issued similar warnings. “The higher horticultural concentrations will work without added salt, but I am strongly opposed to untrained people using those stronger concentrations,” said Strenge.
“5% is relatively harmless to users, but 20% can cause chemical burns,” he said, adding, “As long as users stick with 5% vinegar, the worst human health risk is minor eye-irritation.”
Users are advised to wear goggles and protective clothing while using horticultural vinegars. There is also a risk of chronic bronchitis, dermatitis, and even tooth erosion with repeated use and exposure.
In the End, Is It Worth It?
While organic homemade vinegar weed killers sound quaint, easy, and safe to use, gardeners will run into a couple of obstacles. First: these vinegar solutions are nowhere near as effective as they’d hoped they would be. Second: the potential risks — whether to garden or lawn soil life, or to your own health — may outweigh the benefits.
Again, Strenge’s recommendation is a mixture of vinegar and salt and dishwashing soap for those dead set on making a backyard recipe. But that can also set you up with some soil problems, too, if you’re not careful.
Salt build-up “can become a significant problem from repeated use,” said Strenge, adding that repeated use with salt is the only way for 5% vinegar to be effective. “Table salt can contribute to sodium toxicity and potentially result in loss of other necessary nutrients from the soil.”
Strenge added that Epsom salts — not just table salts — can be used too, but also interfere with lawn and garden health. With all this being said, it may just be easier to pull those weeds out by hand than to use vinegar.